Titanium dioxide-supported mercury photocatalysts for oxidative removal of hydrogen sulfide from the air using a portable air purification unit

Photocatalytic removal of gaseous hydrogen sulfide (H2S) has been studied through the control of key process variables using a prototype air purifier (AP) fabricated with titanium dioxide (TiO2)-supported mercury. The performance of Hg/TiO2 systems, prepared with different Hg mass proportions over TiO2 (such as 0.1%, 1%, 2%, and 5%), is measured against 5 ppm H2S at 160 L min-1 under UV irradiation. Accordingly, their removal efficiency (RE) values after 360 s are 40.3%, 74.8%, 99.3%, and 99.9%, respectively (relative to 33.5% of AP (TiO2)). An AP with a 2% Hg/TiO2 unit achieves a clean air delivery rate of 32 L min-1 with kinetic reaction rate (r (at 10% RE)) of 0.774 mmol h-1 g-1, quantum yield of 2.19E-02 molecules photon-1, and space-time yield of 1.46E-04 molecules photon-1 mg-1. The superior photocatalytic performance of Hg/TiO2 is supported by superoxide anion and hydroxyl radicals formed in dry air and humid nitrogen (N2) environments, respectively. A density functional theory simulation suggests that the presence of oxygen vacancies should promote the disparities in the electronic structure to subsequently affect the reaction pathways and energetics. The presence of moisture enhances the robust formation of a mercury-OH bond to favorably yield β-mercury sulfide from H2S.

Photocatalysts for a sustainable future: Innovations in large-scale environmental and energy applications

The growing environmental and energy crises have prompted researchers to seek new solutions, including large-scale photocatalytic environmental remediation and the production of solar hydrogen using photocatalytic materials. To achieve this goal, scientists have developed numerous photocatalysts with high efficiency and stability. However, the large-scale application of photocatalytic systems under real-world conditions is still limited. These limitations arise at every step, including the large-scale synthesis and deposition of photocatalyst particles on a solid support, and the development of an optimal design with high mass transfer and efficient photon absorption. The purpose of this article is to provide a detailed description of the primary challenges and potential solutions encountered in scaling up photocatalytic systems for use in large-scale water and air purification and solar hydrogen production. Additionally, based on a review of current pilot developments, we draw conclusions and make comparisons regarding the main operating parameters that affect performance, as well as propose strategies for future research.

Recent advances in Metal Organic Framework (MOF)-based hierarchical composites for water treatment by adsorptional photocatalysis: A review

Architecting a desirable and highly efficient nanocomposite for applications like adsorption, catalysis, etc. has always been a challenge. Metal Organic Framework (MOF)-based hierarchical composite has perceived popularity as an advanced adsorbent and catalyst. Hierarchically structured MOF material can be modulated to allow the surface interaction (external or internal) of MOF with the molecules of interest. They are well endowed with tunable functionality, high porosity, and increased surface area epitomizing mass transfer and mechanical stability of the fabricated nanostructure. Additionally, the anticipated optimization of nanocomposite can only be acquired by a thorough understanding of the synthesis techniques. This review starts with a brief introduction to MOF and the requirement for advanced nanocomposites after the setback faced by conventional MOF structures. Further, we discussed the background of MOF-based hierarchical composites followed by synthetic techniques including chemical and thermal treatment. It is important to rationally validate the successful nanocomposite fabrication by characterization techniques, an overview of challenges, and future perspectives associated with MOF-based hierarchically structured nanocomposite.

A review on recent advancements in photocatalytic remediation for harmful inorganic and organic gases

Due to the continuous increase in industrial pollution and modern lifestyle, several types of air contaminants and their concentrations are emerging in the atmosphere. Besides, photocatalysis has gained much attention in the elimination of air pollution. Several ultraviolet and visible light active photocatalysts were tested in air pollutant treatment and thereby, the number of reports was increased in the past few years. In this context, this review describes the photocatalytic treatment of gaseous inorganic contaminants like NO_x, H₂S, and organic pollutants like formaldehyde, acetaldehyde, and benzene derivatives. Different photocatalysts with their air pollutant removal efficiency were explained. Improving strategies such as metal/non-metal doping, composite formation for photocatalyst activities have been studied. Moreover, an analysis is presented from each of the existing photocatalytic immobilization approaches. Also, factors responsible for effective photocatalysis were explained. Overall, the photocatalytic abatement technique is an auspicious way to eliminate different air contaminants. Besides, existing drawbacks and future challenges are also discussed.

One-dimensional metal-organic frameworks for electrochemical applications

Metal-organic frameworks (MOFs) are as a category of crystalline porous materials. Extensive interest has been devoted to energy storage and energy conversion applications owing to their unique advantages of periodic architecture, high specific surface area, high adsorption, high conductivity, high specific capacitance, and high porosity. One-dimensional (1D) nanostructures have unique surface effects, easily regulated size, good agglutination of the substrate, and other distinct properties amenable to the field of energy storage and conversion. Therefore, 1D nanostructures could further improve the characteristic properties of MOFs, and it is of great importance for practical applications to control the size and morphological characteristics of MOFs. The electrochemical application of 1D MOFs is mainly discussed in this review, including energy storage applications in supercapacitors and batteries and energy conversion applications in catalysis. In addition, various synthesis strategies for 1D MOFs and their architectures are presented.

Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO₂ and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis.

Electrospun PU nanofiber composites based on carbon nanotubes decorated with nickel-zinc ferrite particles as an adsorbent for removal of hydrogen sulfide from air

This study focuses on the synthesis of carbon nanotubes decorated with nickel-zinc ferrites and fabrication of polyurethane (PU) nanofiber containing CNT-ferrite composites as highly efficient adsorbents for removal of hydrogen sulfide. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, and powder X-ray diffraction (PXRD) are used to perform microstructural and morphological characterization of the electrospun nanofibrous composites. To show the efficiency of the composite as an adsorbent, a breakthrough test is carried out. It is shown that the PU-CNT-ferrite composites are fabricated almost uniformly with an average fiber diameter of 320 nm and exhibit significant H₂S breakthrough capacity (498 mgH₂S/g) compared to both the pristine PU and PU-CNT nanofibers. These electrospun nanofibers based on CNT-ferrite composites, already studied for H₂S adsorption with promising results, open up new and interesting perspective into the design and fabrication of highly efficient membrane for practical application in the processes of air purification.

The function of metal-organic frameworks in the application of MOF-based composites

In the last two decades, metal-organic frameworks (MOFs), as a class of porous crystalline materials formed by organic linkers coordinated-metal ions, have attracted increasing attention due to their unique structures and wide applications. Compared to single components, various well-designed MOF-based composites combining MOFs with other functional materials, such as nanoparticles, quantum dots, natural enzymes and polymers with remarkably enhanced or novel properties have recently been reported. To efficiently and directionally synthesize high-performance MOF-based composites for specific applications, it is vital to understand the structural-functional relationships and role of MOFs. In this review, preparation methods of MOF-based composites are first summarized and then the relationship between the structure and performance is determined. The functions of MOFs in practical use are classified and discussed through various examples, which may help chemists to understand the structural-functional relationship in MOF-based composites from a new perspective.

Bacteria-Assisted Synthesis of Nanosheet-Assembled TiO2 Hierarchical Architectures for Constructing TiO2-Based Composites for Photocatalytic and Electrocatalytic Applications

Synthesis and application of three-dimensional TiO₂ hierarchical architectures are one of the major priorities in the research and development of TiO₂ catalysts. Using bacteria as a template and a reactor, a bioinspired strategy was developed in the present study to synthesize nanosheet-assembled TiO₂ hierarchical architectures (N-TiO₂-HA) and relative composites for photocatalytic and electrocatalytic applications. In the first part of this work, three kinds of bacteria were used for the synthesis of N-TiO₂-HA with satisfactory monodispersity, and the growth mechanism was investigated. In the second part, porous TiO₂ hollow spheres (P-TiO₂-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in air, were incorporated with MIL-101(Fe) to improve the visible-light photocatalytic efficiency. The results of the photo-Fenton-assisted degradation of rhodamine B and ciprofloxacin indicate that the synthesized composites have excellent visible-light photocatalytic activity. In the third part, the nanosheet-assembled TiO₂-carbon hollow spheres (N-TiO₂-C-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in argon atmosphere, were electrodeposited with Pt for electrocatalytic oxidation of methanol. The electrochemical measurements show that Pt-deposited N-TiO₂-C-HS have better electrocatalytic activity, stability, and tolerance to CO poisoning than commercial Pt/C catalysts.

Overview of Photocatalytic Membrane Reactors in Organic Synthesis, Energy Storage and Environmental Applications

This paper presents an overview of recent reports on photocatalytic membrane reactors (PMRs) in organic synthesis as well as water and wastewater treatment. A brief introduction to slurry PMRs and the systems equipped with photocatalytic membranes (PMs) is given. The methods of PM production are also presented. Moreover, the process parameters affecting the performance of PMRs are characterized. The applications of PMRs in organic synthesis are discussed, including photocatalytic conversion of CO2, synthesis of KA oil by photocatalytic oxidation, conversion of acetophenone to phenylethanol, synthesis of vanillin and phenol, as well as hydrogen production. Furthermore, the configurations and applications of PMRs for removal of organic contaminants from model solutions, natural water and municipal or industrial wastewater are described. It was concluded that PMRs represent a promising green technology; however, before the application in industry, additional studies are still required. These should be aimed at improvement of process efficiency, mainly by development and application of visible light active photocatalysts and novel membranes resistant to the harsh conditions prevailing in these systems.

Conductive Ti3C2 and MOF-derived CoSx boosting the photocatalytic hydrogen production activity of TiO2

We report a novel TiO₂ nanocrystals photocatalyst confined by ZIF-67-templated porous CoS_x, with conductive Ti₃C₂ boosting the transport efficiency of the charge carriers.